Screws subjected to high mechanical and thermal loads are used, for example, in gas turbine construction. An example of application is the fastening of a combustion-chamber inner lining to a wall of a combustion chamber.
It is normally attempted to operate a gas turbine with as high a temperature as possible in the combustion chamber in order to achieve a high efficiency. Gas temperatures of 1200° C. to 1300° C. are typically achieved at the outlet of the combustion chamber. The combustion-chamber inner lining is often fastened to the combustion-chamber wall with screws inserted from the inside, i.e. from the combustion chamber. The head of the screws is therefore directly exposed to the fuel gas in the combustion chamber. If the screw or a part of the screw, in particular the screw head, due to a failure of said screw, gets into the combustion chamber and is entrained by the gas flow, serious damage to the downstream turbine is the result.
In order to reliably prevent failure of the fastening screws arranged in the combustion chamber, the screws can be designed to be coolable. To this end, the fastening screw has, for example, an axial bore through which a cooling fluid, in particular cooling air, is directed into the combustion chamber from the outside of the latter. The cooling fluid mixes with the fuel gases in the combustion chamber. As a result, the temperature in the combustion chamber is undesirably reduced. The loss of efficiency associated therewith is tolerated in order to ensure sufficient strength of the fastening screws by means of the cooling. However, ensuring sufficient mechanical loading capacity of the fastening screws means a considerable coolant requirement.